Epidemiology for English speaking students / Tasks for Seminars / Seminar 3 Analitical studies / Tasks 2

Task 1

Tab. The number of new cases of an arterial hypertension (AH) in Moscow among the women aged 20-69 years, depending the presence or absence of high cholesterol level.

	new cases of a AH
Groups	Yes	no	total
The main group - HCL is high	64	79	143.
The control group – HCL is normal	219	815	1034
In total	283	894	1177

Note: the difference in frequency of new cases of a AH in experimental and control groups is significant (р < 0,05)

1. Indicate possible omission in the title of the table. Name the type of the table. Indicate, what terms should be used to designate design of the given study.

2. Define the purpose of this study.

3. Indicate what values help to calculate the data of this table and decipher their epidemiological meaning.

1. Explain, the meaning of the terms internal and external significance of the data of epidemiological study and whether it is possible to extrapolate the results of this study on all women 20-69 years.

Task 2

tab. Occurrence of frequent episodes of quinsy in the anamnesis of rheumatoid arthritis patients and in the anamnesis healthy people.

	often anginas (2 and more yearly)		total
Groups	Yes	no
Rheumatoid arthritis patients	54	30	84
Healthy people	1314	5904	7218
In total	1368	5934	7302

The notice: difference in quinsy episodes frequency in rheumatoid arthritis patients and in the anamnesis healthy people is significant

1. Indicate possible drawbacks in the title of the table.

Name the type of the table. Indicate, what terms it is necessary to designate the design of the given study And also explain its main stages.

2. Define the aim of the study.

3. Indicate, what ratios help to calculate the data of this table and decrypt decipher their epidemiological meaning

4. Explain, the meaning of the terms internal and external significance of the data of epidemiological study and whether it is possible to extrapolate the results of this study on all rheumatoid arthritis patients.

Task 3

Hepatocellular adenoma (HCA), a rare type of benign though potentially fatal liver tumor, is

associated with long term oral contraceptive (OC) use, especially in older women. A case comparison

study showed that the effect of duration of OC use on the risk of developing HCA

is marked:

Duration Rate ratio

Duration	Relative risk
1 or less	1*
4 years	9
4-7 years	120
8+ years	500

* Reference level (includes none)

(Source: Armed Forces Institute of Pathology and Center for Disease Control. Increased risk of hepatocellular adenoma in women with long term use of oral contraceptive. Morbidity and Mortality Weekly Report 26 (36):293-294, September 9, 1977, cited in Oral Contraceptives, Population Reports Series A, Number 5, January 1979.)

Assuming that the incidence density (ID) of HCA for one year or less use of OC is 0.06/100,000 per year (i.e., 6 per 10,000,000 women-years), what are the attributable rate (rate difference) over baseline and the attributable rate proportion associated with each duration category of OC use?

Interpret these measures and state what implications you might draw. (For this question, use the attributable risk formulas.)

Task 4

In a study of adverse effects of radiotherapy among immigrant children in Israel (Ron E, Modan B, and Boice JD. Mortality after radiotherapy for ringworm of the scalp. Am J Epidemiol 1988:127:713-25), 10,834 irradiated children were identified from original treatment records and matched to 10,834 no irradiated, tinea-free comparison subjects selected from the general population. Follow-up was accomplished using the Israeli Central Population Registry, which enabled nearly all subjects to be followed forward in time (retrospectively) for a mean of 26 years following age at irradiation. Computation of person-years of observation began at the date of treatment for tinea capitis, or the equivalent date for the matched comparison subjects, and ended at the date of death for those who died or May 31, 1982 for those not known to have died. Person-years of observation were: irradiated subjects, 279,901 years; comparison subjects, 280,561 years. During the follow-up there were 49 deaths from cancer in irradiated subjects, and 44 in the nonirradiated population comparison subjects .

1 Present the results of the study as 2×2 table.

2 a. What are the rates of cancer death in the two groups?

b. Calculate and describe in one sentence the incidence density ratio for cancer death comparing irradiated and nonirradiated subjects?

c. Assuming causality, estimate how many cancer deaths per 100,000 person years of follow-up of irradiated subjects were attributable to radiotherapy.

For these questions, use the attributable risk formulas:

d. Again assuming causality, what proportion of cancer deaths in irradiated subjects were due to radiation therapy?

e. If 10% of this population had received radiotherapy for tinea capitis, what proportion of all cancer deaths within the relevant age span (mean age 7 to 33 years) would be due to radiation therapy?